| 摘要 |
<p>PROBLEM TO BE SOLVED: To perform the feedback control of an air-fuel ratio while retaining the durability of air-fuel ratio sensors by using the air-fuel ratio sensor upstream an auxiliary catalyst in a bypass pass when the bypass pass is opened, and using the air-fuel ratio sensor upstream a main catalyst in a main pass when the bypass pass is closed. SOLUTION: Air fuel ratio sensors 12, 13 are arranged on respective upstream sides of a main catalyst convertor 10 and an auxiliary catalyst convertor 11. The feedback control of air-fuel ratio is performed by using the air-fuel ratio sensor 13 upstream the auxiliary catalyst 11 when a bypass pass is opened, and using the air-fuel ratio sensor 12 upstream the main catalyst 10 when the bypass pass is closed. The air-fuel ratio sensors 12, 13 used according to the opening/closing conditions of the bypass pass, are thusly elected, therefore, the feedback control of the air-fuel ratio can be performed with excellent accuracy when the bypass pass is closed. When the bypass pass is closed, distance from an exhaust port to the air-fuel ratio sensors can be lengthened, thus, the feedback control of the air-fuel ratio can be carried out while retaining the durability of the air-fuel ratio sensors.</p> |
